SRC/claed0.f(3)

NAME
SRC/claed0.f

SYNOPSIS

  Functions/Subroutines
subroutine claed0 (qsiz, n, d, e, q, ldq, qstore, ldqs, rwork, iwork, info)
CLAED0 used by CSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Function/Subroutine Documentation

  subroutine claed0 (integer qsiz, integer n, real, dimension( * ) d, real, dimension( * ) e, complex, dimension( ldq, * ) q, integer ldq, complex, dimension( ldqs, * ) qstore, integer ldqs, real, dimension( * ) rwork, integer, dimension( * ) iwork, integer info)

CLAED0 used by CSTEDC. Computes all eigenvalues and corresponding eigenvectors of an unreduced symmetric tridiagonal matrix using the divide and conquer method.

Purpose:

    !>
    !> Using the divide and conquer method, CLAED0 computes all eigenvalues
    !> of a symmetric tridiagonal matrix which is one diagonal block of
    !> those from reducing a dense or band Hermitian matrix and
    !> corresponding eigenvectors of the dense or band matrix.
    !>

Parameters
    QSIZ

    !>          QSIZ is INTEGER
    !>         The dimension of the unitary matrix used to reduce
    !>         the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1.
    !>

    N

    !>          N is INTEGER
    !>         The dimension of the symmetric tridiagonal matrix.  N >= 0.
    !>

    D

    !>          D is REAL array, dimension (N)
    !>         On entry, the diagonal elements of the tridiagonal matrix.
    !>         On exit, the eigenvalues in ascending order.
    !>

    E

    !>          E is REAL array, dimension (N-1)
    !>         On entry, the off-diagonal elements of the tridiagonal matrix.
    !>         On exit, E has been destroyed.
    !>

    Q

    !>          Q is COMPLEX array, dimension (LDQ,N)
    !>         On entry, Q must contain an QSIZ x N matrix whose columns
    !>         unitarily orthonormal. It is a part of the unitary matrix
    !>         that reduces the full dense Hermitian matrix to a
    !>         (reducible) symmetric tridiagonal matrix.
    !>

    LDQ

    !>          LDQ is INTEGER
    !>         The leading dimension of the array Q.  LDQ >= max(1,N).
    !>

    IWORK

    !>          IWORK is INTEGER array,
    !>         the dimension of IWORK must be at least
    !>                      6 + 6*N + 5*N*lg N
    !>                      ( lg( N ) = smallest integer k
    !>                                  such that 2^k >= N )
    !>

    RWORK

    !>          RWORK is REAL array,
    !>                               dimension (1 + 3*N + 2*N*lg N + 3*N**2)
    !>                        ( lg( N ) = smallest integer k
    !>                                    such that 2^k >= N )
    !>

    QSTORE

    !>          QSTORE is COMPLEX array, dimension (LDQS, N)
    !>         Used to store parts of
    !>         the eigenvector matrix when the updating matrix multiplies
    !>         take place.
    !>

    LDQS

    !>          LDQS is INTEGER
    !>         The leading dimension of the array QSTORE.
    !>         LDQS >= max(1,N).
    !>

    INFO

    !>          INFO is INTEGER
    !>          = 0:  successful exit.
    !>          < 0:  if INFO = -i, the i-th argument had an illegal value.
    !>          > 0:  The algorithm failed to compute an eigenvalue while
    !>                working on the submatrix lying in rows and columns
    !>                INFO/(N+1) through mod(INFO,N+1).
    !>

Author
    Univ. of Tennessee

    Univ. of California Berkeley

    Univ. of Colorado Denver

    NAG Ltd.

Definition at line 143 of file claed0.f.

Author

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